In European patent application EP 0 595 178 a device for electrolytic wastewater treatment having vertical electrodes is described. It is indicated in this document that the electrolysis uses a direct current, a soluble iron anode and a suspension or dust of “coke” particles (cf. page 3, column 4, lines 32 and 34) with a view to producing a galvanic coagulation.
U.S. Pat. No. 4,014,766 relates to a process for treating raw waters using a device having a vertical cathode and an anode containing iron turnings (column 3, line 5), so as to give rise to a flocculation of iron hydroxide. The floc is then oxidized.
In French patent application No. FR 2 459 067, a plant for the electro-purification of waters, is described in which electrocoagulation is produced by means of electrodes constituted of baskets containing scrap iron (page 5, lines 10, 11).
The United States patent published under the No. US 2005/0167285 relates to the removal of arsenates contained in drinking water. It mentions the formation of a metal hydroxide via anodic dissolution (page 3, paragraph [0046]) of an anode which may be made of mild steel or stainless steel (paragraph [0048]).
Document JP 51150866 discloses a process for disposing of wastewater containing Cr6+ ions, in which these ions are electrolytically reduced to Cr3+ ions in a device having a vertical cathode surrounding particles contained in a receptacle.
United States patent application No. US 2006/0000784 describes a process for treating wastewater in several steps. A first step may consist in obtaining an intermediate effluent, for example by coagulation or flocculation (page 2, left-hand column, line 2). In a second step, it is possible to treat the intermediate effluent by using (paragraph [0021]):                either a spontaneous electrochemical treatment, in which sacrificial iron scrap that is activated, preferably by ferric ions, is used; these ferric ions may be formed by oxidation of metallic iron or of ferrous ions using, in particular, active chlorine;        or an electrochemical treatment that takes place in a non-spontaneous manner, by applying electric tension to a sacrificial metal or to ferrous ions.        
In U.S. Pat. No. 5,578,200, the coagulants customarily used are cited. These are, in general, inorganic coagulants such as aluminum sulfate, aluminum chloride and ferric chloride. The aforementioned United States patent application No. US 2006/0000784 also mentions (paragraph [0015]) the use of sacrificial metals which may be, besides iron and aluminum, nickel, cobalt, zinc, copper and combinations thereof.
More than ten years ago already, the inventor of the present patent application developed the process for pretreating raw waters that is the subject of the French patent application published under the number FR 2 740 129.
This process comprises a step of shock chlorination using hypochlorite then a step of thorough disinfection by electrolysis of iron particles which may be contained in titanium or zirconium baskets covered with a catalyst and stirred mechanically or ultrasonically.
During this thorough disinfection, the water to be treated is electrolyzed using an alternating current, with a view to reducing the residual active chlorine. The residual hypochlorite remaining in the water to be treated, the concentration of which is very low, of the order of 1 to 5 ppm, is also electrolyzed at the same time.
The inventor has continued its research with a view to improving its process and integrating the new standards regarding drinking water, in particular the European standard DWD 98/83/EC, and also the latest recommendations of the World Health Organization (WHO) in this field.
The inventor has thus succeeded in developing novel processes, devices and plants capable of pretreating waters of an even more degraded quality than before, having higher loadings of sludges, salts, nitrites, organic compounds and/or heavy metals.